Magnetron tubes having adjustable frequency



y 1957 A. LEBLOND 2,799,803

MAGNETRON TUBES HAVING ADJUSTABLE FREQUENCY Filed March 31, 1955 *3 Sheets-Sheet l A. LEBLOND 7 2,799,803

MAGNETRON TUBES HAVING ADJUSTABLE FREQUENCY July 16, 1957 3 Shets-Sheet 2 Filed March 51, 1955 MAGNETRON TUBES HAVING ADJUSTABLE FREQUENCY Filed March 51, 1955 A. LEBLOND 'July 16, 1957 3 Sheets-Sheet 3 United States 3m MAGNETRON TUBES HAVING ADJUSTABLE FREQUENCY Andr Leblond, Paris, France, assignor to Compagnie Generale dc Telegraphic Sans Fil, a corporation of France Application March 31, 1955, Serial No. 498,417

Claims priority, application France April 10, 1954 Claims. or. 315-3973) Oscillators or" the magnetron type generally have a relatively fixed operating frequency governed by their constructional characteristics. It is difficult to construct magnetrons having a frequency which is adjustable over a suitably widetuning range.

A type of magnetron having a single cavity resonator has already been suggested for this purpose, wherein the resonator is in the shape of a cylinder of revolution closed by .two covers disposed respectively on its lower and upper faces. A circular interdigital anode structure is located in thiscylin'der coaxially therewith, the cavity resonator of the magnetron being thus bounded by the wall of the cylinder, the covers and the interdigital anode structure.

As is'well kn'ownzin the art such an anode structure comprises two sets, .or combs of regularly-spaced fingers, the fingers of the first set resting on one of the covers and the fingers of the other set on the other cover. The cathode is disposed in the central part of the tube. v

In such tubes, the operatin'gfrequency is'modified by moving one ofthe covers toward and away from the other which remtains stationary relative to the envelope or the tube. The translation. of the first cover is effected along the axis of the magnetron. This system has several disadvantages.

The cylindrical surface of the cavity resonator needs to be deformable, which is difiicult'to realise; further,

the tuning range thereby obtained is small. The height of the interaction space of the tube is variable. There are modifications and distortions of the electromagnetic field in this space. This detracts from the efiicient operation of the tube.

The present invention has for its object to provide a magnetron tube of the above-mentioned type in which such disadvantages are in a large measure avoided.

The magnetron tube in accordance with the invention comprises a cavity resonator bounded externally by a cylindrical wall and internally by an interdigital anode structure coaxial with the cylindrical Wall, and other anode structure being rotatably mounted within the reso nator coaxially with the first delay line.

Means are provided for adjusting, from without the tube, the position of the second anode structure with respect to the first anode structure and thereby to adjust the operating frequency of the tube.

The invention will be better understood from the ensuing description with reference to the accompanying drawings in which:

Fig. 1 is a sectional view in a plane containing the axis of a cylindrical magnetron embodying the invention;

Figs. 2 and 3 are sectional views taken along planes 2-2 and 3-3 respectively perpendicular to the axis of the magnetron shown in Fig. 1;

Fig. 4 is a longitudinal sectional view of another embodiment of the invention; and

Fig. 5 is a cross-sectional view of still another embodiment of the invention.

Fig. 1 illustrates a magnetron of cylindrical structure comprising a vacuum-tight envelope formed of a hollow metallic cylinder of revolution 1, closed at its upper and lower end faces by two glass covers 101. Provided on the cylinder 1 are two circular recesses 2 and 3 in which are respectively fixed, by means of screws 6 and 7, two annular plates 4 and5 which are coaxial with the envelope 1. These two plates carry, along the periphery of their respective apertures, the elements of a first interdigital anode structure, for example interdigitated fingers ,8 and 9 which form two combs of a first interdigital anode structure which will be termed hereinafter the interior interdigital anode structure.

Provided respectively in the plates 4 and 5 are two annular recesses 20 coaxial with the tube. In these recesses is rotatably mounted a hollow metallic cylinder of revolution 12 coaxial with the envelope 1. Fixed on the cylinder, by means of screws 15 and 15 are the elements of a second interdigital anode structure, for example a further two combs formed respectively of fingers 13 and 14. The latter constitute another interdigital anode structure termed hereinafter the exterior interdigital anode structure. A notch or recess 17 is provided in the cylinder 12 mid-way between the plates 4 and 5. Engaged in this aperture is the curved end of a rigid rod 18 which extends through the envelope 1 of the magnetron through an aperture 19 as shown in Fig. 3. The unit 12-43-14 is capable of being rotated through .a certain angle, bymeans of the rod 1% controlled from the exterior, relative to the interior interdigital anode structure which comprises the fingers 9 and 8 and is rigid with the envelope of the magnetron. The position of the rod 18 may be adjusted by rotating a knurled knob 33 having ascrew thread 34. A deformable envelope 35 of a well known type renders the device perfectly liquidand gas-tight. A coaxial cable 22 extends through the envelope.1 of the magnetron through an aperture 23 as shown in Fig. 1. The central conductor 24 thereof is connected to an extension 25 of one of the fingers 21 of the interior anode structure. Two other apertures 26 and 27 are providedin the envelope 1 of the magnetron to permit the passage of connections to thefilaments, which also support the .cathode 28 coaxial with the envelope 1. Ceramicplugs 23, 26' and 27 close the apertures 23, 26 and 27. The heating current is brought to the cathode 28 by conductors 29 and 3% from a source 31. A second source of voltage 32 furnishes the fixed potential difference between the envelope 1, which is grounded, and the cathode 28 necessary for the operation of the tube. A magnet or an electromagnet (not shown) directs, as well known, a uniform magnetic field B along the axis of the tube in the space between the anode and the cathode 28.

Fig. 2 shows apertures 11 for evacuating the space between cylinders 1 and 12.

The tube operates in the following manner:

The cylinder 12 and the interior anode structure form a cavity resonator having a well-defined resonant frequency. The exterior anode structure is movable inside the cavity of this resonator.

Each position of the exterior anode structure relative to the interior anode structure corresponds to a particular configuration of the electromagnetic field in the cavity. Thus, each one of these positions corresponds to an operational frequency of the magnetron.

When the exterior anode structure is rotated through an angle such that a finger S occupies the position previously occupied by the immediately adjacent finger 8, the field will regain its original configuration.

Thus it may be seen that, if N is the total number of V 3 fingers of the exterior anode structure, a rotation of this anode structure through an angle .of

Applicant has found that the tuning rage of the magnetron depends mainly on: the height of the fingers of the two anode structures, the length of interpenetration of the combs, the radius of the cylinder. 12, and the number of elements in each anode structure.

It is obvious that the greater the number of fingers in eachanode structure, the smalleris the angle through which it is necessary to rotate oneof the anode structures relative to the other for covering the entire frequency band in which the magnetron is likely to operate. Some types of anode structure which may be used in accordance with the invention are described in copending applications filed March 11, 1952, Serial No. 275,928, April 17, 1952, Serial No. 282,761, now Patent No. 2,770,780, and April 17, 1952, Serial No. 282,762. Althoughthe invention may be used to particular advantage with interdigital anode structures of these or other types, it is to be understood that it is also applicable to any other type of interdigital anode structure suitable for use in tubes of the magnetron type.

Figs. 4 and 5 relate to other embodiments of the invention.

7 Fig. 4 shows a tube similar to that of Figs. 1, 2, 3 wherein the two interdigital anode structures have fingers, the height of which differs from one anodestructure to the other. The number of fingers is the same in both anode structures. Fingers 89 of the interior anode structure have a larger height than fingers 1314 of the exterior anode structure.

4 (b) The dimensions of the interaction space are constant.

What is claimed is:

1.'An electronic oscillator tube, of the magnetron type, having in a vacuum tight enclosure, an elongated cathode for emitting an electronic cloud, and a single cavity resonator, said cavity resonator comprising an exterior cylinder having a smooth surface and w axial with said cathode, two covers closing respectively the end faces of said cylinder, and within said cylinder a first and a second interdigital anode structure coaxial with said cathode, said first anode structure being rotatably mounted with respect to said second anode structure. r

2. In an electronic oscillating tube of the magnetron type a tuning device comprising: an outer cylinder having a central axis; a first and a second conducting plane disks perpendicular to said central axis, fixed with respect to said outer cylinder and spaced with respect to each other; two first combs fixed, respectively to said conducting plane disks and extending across the space therebetween to form a first interdigital anode structure; a hollow cylinder coaxially mounted with said outer cylinder and bounded by said two plane disks; two second combs fixed to said hollow cylinder forming a second interdigital anode structure coaxial with said first anode fingers but the height of the latter differs from one anode Fig. 5 shows a tube similar to that of Figs. 1, 2, 3

wherein the two interdigital anode structures have numbers of fingers which differ from one anode structure to the other. The exterior anode structure has more fingers than the interior anode structure. The height of fingers References Cited in the file of this patent UNITED STATES PATENTS Hagst'rum Apr. 8, 1947 Crawford Apr. 14, 1953 

